1. Field of the Invention
The present invention relates to a motion-and nonstandard adaptive three-dimensional YC separating circuit for separating a National Television System Committee (NTSC) composite video signal into a luminance signal (hereinafter, referred to as a Y signal) and a chroma signal (hereinafter, referred to as a C signal).
2. Description of the Related Art
A prior art three-dimensional YC separating circuit includes an intra-field YC separating circuit using line memories and an inter-frame YC separating circuit using a frame memory.
In a static image, a correlation between two adjacent frames is strong, so that the inter-frame YC separating circuit is selected to carry out a YC separation. Conversely, in a dynamic image, a correlation between two adjacent frames is weak, so that the inter-frame YC separating circuit cannot be used, and therefore, the intra-field YC separating circuit is selected to carry out a YC separation.
In order to discriminate a dynamic image part of an image from a static image part thereof, a motion detecting circuit is provided in the prior art YC separating circuit.
Also, if an NTSC composite video signal is a standard signal used in television broadcasting, a reproduction in a laser disk player, and the like, which completely satisfies the NTSC specification, the following interleave relationship between the Y signal and the C signal is satisfied: ##EQU1##
where f.sub.SC is a color sub-carrier frequency;
f.sub.H is a horizontal frequency; and
f.sub.V is a vertical frequency. Conversely, if the NTSC composite video signal is a nonstandard signal used in a reproduction in a home video apparatus, an output of a television game apparatus, and the like, which does not completely satisfy the NTSC specification, the above-mentioned interleave relationship is not satisfied, so that the inter-frame YC separating circuit cannot be used. Therefore, in this case, the intra-field YC separating circuit is selected to carry out a YC separation.
In order to discriminate an NTSC standard signal from an NTSC nonstandard signal, a standard/nonstandard detecting circuit is provided in the prior art three-dimensional YC separating circuit.
Thus, in the prior art three-dimensional YC separating circuit, the selection of the intra-field YC separating circuit and the inter-frame YC separating circuit is carried out as follows:
______________________________________ STATIC IMAGE DYNAMIC IMAGE ______________________________________ STANDARD INTER-FRAME INTRA-FIELD SIGNAL NONSTANDARD INTRA-FIELD INTRA-FIELD SIGNAL ______________________________________
Note that the intra-field YC separating circuit has a S/N improvement effect, i.e., a noise reduction effect for only a definite frequency bandwidth, while the inter-frame YC separating circuit has a noise reduction effect for all of the frequencies, as will be explained later in detail. In the above-mentioned prior art three-dimensional YC separating circuit, however, the inter-frame YC separating circuit is used only for a standard NTSC composite video signal for a static image part of an image, and therefore, effective use is not made of the inter-frame YC separating circuit.